Up to the present, a cell-free protein synthesis system (i.e., an in vitro protein synthesis system) has been known as a technique of protein synthesis. Alternatively, a protein synthesis system comprising introducing a gene encoding a protein of interest into a live cell and separating and purifying the protein synthesized in a cell or culture solution is also known. In the case of the latter protein synthesis system, disadvantageously, it has been impossible to synthesize a protein that inhibits the growth of a cell to be used. In a cell-free protein synthesis system, however, a protein that is toxic to live cells can be synthesized.
In the cell-free protein synthesis system, however, it is known that some types of proteins are difficult to synthesize or cannot be synthesized in sufficient amounts. JP Patent Publication (kokai) No. H05-076381 (1993) A discloses a method for maintaining an energy source in order to accelerate a cell-free protein synthesis reaction, although such method is not always effective for proteins that are difficult to synthesize. As a method for synthesizing proteins that are difficult to synthesize, JP Patent Publication (kohyo) No. 2006-508672 A discloses a technique for modifying a DNA (mRNA) sequence. Such technique, however, lacks versatility since it must be exclusively designed for a relevant protein. JP Patent Publication (kokai) No. H11-056363 (1999) A discloses a technique in which large quantities of template DNA are contained in a reaction system so as to increase the amount of proteins synthesized. Such technique, however, would not enable the synthesis of proteins that are difficult to synthesize, and the effects of increasing the amount of proteins synthesized are not satisfactory.